1. Field of the Invention
The present invention relates to devices for changing transmission fluid, and more particularly to devices that compare a condition of used fluid being removed with the condition of fresh fluid being added to determine when the used fluid in a transmission has been substantially replaced by fresh fluid.
2. Description of the Prior Art
Automatic transmissions require transmission fluid because such fluid is employed in part as a driving means within the transmission and is additionally employed to lubricate the internal components within such transmissions. Over time such fluid becomes less viscous and thus less efficient in lubricating such components. Additionally, the fluid tends to pick up contamination in the form of metal particles and the like, thus exposing the transmission to accelerated wear. It is therefore desirable to periodically exchange the used fluid with new fluid to maintain the viscosity of such fluid within the transmission and to maintain the cleanliness of the transmission to thereby increase the useful life of the transmission. A substantially complete exchange of fluid is preferred so that the used fluid as well as undesirable foreign matter contained therein is completely removed from the transmission and is replaced with new, more viscous fluid.
There has been a long standing need for a device which may efficiently perform a substantially complete exchange of transmission fluid in an automatic transmission while at the same time posing minimum risk of damage to the transmission. The conventional method, still widely practiced today, is to simply replace the fluid housed in the pan of the transmission. The pan typically holds from 1 to 5 quarts of the total 7 to 15 quart capacity of the transmission. Thus emptying the pan and then adding that amount of new fluid only serves to dilute the used fluid with some 15-25% of new fluid. Hence this conventional service is quite inefficient since it only serves to mix new fluid with a large quantity of used fluid. Furthermore, this service requires the removal of the transmission fluid pan from the transmission for emptying of the fluid therefrom and replacement of the pan on the transmission housing. This can prove to be a messy and time consuming process. In addition, the pan is often not replaced squarely over the pan seal or, on occasion, will trap small foreign particles in the seal area resulting in leakage.
More recently, there have been efforts to make a complete exchange of all the fluid in an automobile's transmission by disconnecting a fluid tube and draining the fluid into a waste oil dump while manually pouring new fluid into the transmission dipstick tube. This procedure has proven to be inefficient, inadequate and so time consuming that it has failed to gain broad acceptance.
Another method proposed involves disconnecting a transmission fluid cooler line to allow one disconnected end to drain freely, while the other end is connected to a relatively large pressurized bulk storage tank to inject unused fluid into the cooler line to refill the transmission. This procedure can be quite untidy and has proven to be generally unsatisfactory.
Yet another device proposed in an attempt to facilitate fluid removal and replacement in an automobile fluid system includes a switching control device permanently mounted to an engine oil system. A device of this type is described in U.S. Pat. No. 5,056,621 to Trevino. This device includes a pump to be mounted to the engine block and a pair of input suction conduits for connection to, respectively, an oil drain port and to a source of unused oil. The device includes a switch which allows for the selection of the conduit through which fluid will be drawn and a pump to draw fluid through the selected conduit. An output conduit is also provided with a free distal end for releasable connection to a waste oil tank when the switch is in the position to flow fluid from the oil drain port, and for releasable connection to an oil filler tube when the switch is placed in the position to allow fluid to flow from the source of unused fluid. Devices of this type have not gained acceptance for changing transmission fluid in that they are burdensome to use and time consuming because, in order to switch such a device between withdrawing and replacing fluid, the operator must manually remove the output conduit from the waste oil tank and connect such conduit to the vehicle's oil filler tube.
Other work in this field has led to the proposal of a transmission fluid changer including air pressurized tanks for the delivery and extraction of transmission fluid via the transmission cooler lines. A device of this type is shown in U.S. Pat. No. 5,318,080 to Viken. Such devices are rather cumbersome and make no provision for electronically sensing the condition of the fluid being evaluated to determined when the condition of the fluid in the transmission reaches an acceptable level of cleanliness.
Further efforts have led to a portable device which may perform a simultaneous, substantially complete exchange of transmission fluid. Such a device is shown in U.S. Pat. No. 5,370,160 issued to Parker and assigned to the assignee of the instant application. Such a device may be utilized to adjust flow rates of the fluids being withdrawn from or introduced to the transmission. While having gained general commercial acceptance, this device suffers the shortcoming that the operator must rely on either a count of the volume of fluid exchanged or color of fluid being evaluated to indicate when the exchange is substantially complete. Still further efforts have led to the development of a device touted as a portable shown in U.S. Pat. No. 5,337,708 to Chen. The operator of this device is also left with no reliable way of knowing when the exchange of fluid is substantially complete.
The devices described previously all suffer from the common shortcoming that they measure the amount of fluid drained out, or alternatively rely on the operator's subjective comparison of the color of fresh fluid with that of the drained fluid, to indicate when the exchange of used fluid is complete. As described previously, the configuration of most transmissions is such that only a percentage of the fluid can be typically drained out and neither of these two methods is therefore sufficiently accurate to ensure that a satisfactory percentage of the used fluid has been removed. Comparing colors is a highly subjective call, and even an experienced mechanic can be quite inaccurate when the color of the fresh fluid is so dark that even heavily contaminated fluid appears only slightly darker. Comparing the amount of fluid removed with the total amount of fluid the transmission is known to hold is also no guarantee that some of the fluid removed is not just freshly added fluid. Neither method can thus give a reasonably accurate indication of how much of the used fluid has actually been replaced and how much still remains within the transmission.
It has been recognized that small samples of fluid may be taken and dripped into a tiny disk to be sensed by a dielectric sensor to determine the degree to which the fluid so dripped has been contaminated. Such a device has been marketed under the trade designation OilCheck by ICC Federated. However, such an approach has not been generally accepted in the field for detecting the progress made in the exchange of transmission fluid and is generally too untidy and time consuming to employ in the practical applications.
As such, it may be appreciated that there continues to be a need for an automatic transmission fluid exchanging device that will detect and measure the level of contamination in fluid drained from a transmission and thereby enable the operator to know with reasonable accuracy when a certain percentage of the total fluid within the transmission has been replaced. Further, it would be helpful if this capability were employed in a system providing for a continuous and simultaneous exchange of fluid and where the exchange is automatically discontinued upon the fluid in the transmission reaching a predetermined level of renewal. The instant invention addresses this need.